The present invention relates to an apparatus for producing a thin-film photoelectric transducer comprising an integrated assembly of unit cells, each made of thin semiconductor films, such as amorphous silicon (hereinafter a-Si) layers.
Photoelectric transducers using a-Si have attracted the increasing attention of researchers, since a-Si layers having desired shapes and covering large areas can be easily produced by plasma-assisted CVD techniques. In order to generate large voltages and currents, the transducers usually consist of an integrated assembly of unit cells, typically as shown in FIG. 2. In FIG. 2, a unit photoelectric cell 20 is formed by successively depositing a transparent electrode film 22, an a-Si photoactive layer 23 and a metal electrode layer 24 on a glass substrate 21, and a plurality of such unit cells are connected in series. In order to provide the illustrated pattern on a single glass substrate 21, the respective layers 22, 23 and 24 are first deposited on the entire surface of the substrate and are subsequently subjected to chemical etching procedures. Instead of chemical etching processes, U.S. Pat. No. 4,292,092 proposes a laser scribing technique that enables high-speed patterning with a narrow laser beam. As the area of the substrate increases, not only does it become difficult to ensure uniform and precise patterning by the chemical etching techniques, but also larger-scale equipment which requires complicated operating procedures becomes necessary. On the other hand, the laser scribing technique provides a higher accuracy in patterning and is highly adaptable to automation.
A further problem associated with the formation of an a-Si layer 23 on a large substrate 21 is in the increased probability of the creation of defects, such as pinholes, in the a-Si layer. The presence of many pinholes will cause shorting of top and bottom electrodes 22 and 24, thereby decreasing the yield of acceptable devices. It is, therefore, necessary to ensure high product yields by detecting and eliminating any defects in the a-Si layer. While microscopic observations are commonly used for detection purposes, other methods are also known, such as by scanning the surface of the a-Si layer to determine its photocurrent distribution, or by causing an electric current to flow through the a-Si layers to measure the amount of heat generated at shorted points. Any detected defects may be burnt out with a laser beam or by application of a reverse bias voltage. As the use of substrates with larger areas increases, it becomes even more important to provide efficient methods for patterning the individual layers that constitute the photoelectric transducer, detecting any defects in the a-Si layer, and eliminating defects if there are any.